In order for Xenopus spinal neurons to develop normally, spontaneous elevations in cytosolic Ca2+ encompassing the entire growth cone must occur at specific frequencies. The cause of such large scale elevations in Ca2+ (Global Lamellipodial Transients, GLTs) remain unknown though, and is one of the broad goals of this study. This proposal examines a novel event termed a LLT (Localized Lamellipodial Transient), which is also a spontaneous, cytosolic elevation in Ca2+, but on a much smaller and two rapid scale. The specific aims include characterizing the dependence of LLTs on the developmental stage of the cell, as well as the substrate and ionic dependence of the signaling. In addition, the role of Ca2+ release from internal stores will be investigated. Finally, one of the main objectives of the proposal is to determine if GLTs are influenced by, triggered by, or are the summation of, LLTs in the cell. Rapid confocal imaging of spinal neurons in vitro loaded with fluo-4 AM under a variety of pharmacological conditions and times in culture will shed light on these specific aims.